Clostridium difficile is a Gram-positive, rod shaped, anaerobic spore-forming bacterium. The first fully sequenced C. difficile genome was published in 2006 [1] and 3776 predicted coding sequences were identified. C. difficile is a normal component of the gut flora, estimated to be present in 3% of the general population without signs of disease. In situations where the natural balance of the gut flora is disturbed, then C. difficile can become more prevalent. This overgrowth causes the bacterium to start producing toxins under the control of a quorum signalling regulator. The most frequent cause of a disruption to the natural balance of the gut flora is the administration of antibiotics which are deleterious to some gut bacteria, but which do not affect C. difficile. C. difficile is the primary cause of antibiotic associated diarrhoea (AAD), though symptoms may extend to life-threatening pseudomembraneous colitis. The highest prevalence of infection is in elderly hospitalised patients, though infections are on the increase in non-typical groups, such as adolescents and pregnant females [2]. It is has been observed that between 12% and 35% of those infected with C. difficile relapse within 2 months [3].
C. difficile was only identified as the causative agent of AAD in the 1970s. Since then a number of strategies for combating the infection have been attempted. Specific antibiotics, such as vancomycin, metronidazole, nitazoxanamide, bacitracin or fusidic acid were used initially to treatment for C. difficile infection, and continue to be employed today (see references 4, 5 and 6). Widespread treatment with these antibiotics is not favoured, though, due to the risk of C. difficile and also other gut bacteria becoming resistant over time. Recently, treatment with vaccines based upon the toxoids secreted by the bacterium and passive immunotherapy targeting such toxins have been adapted (references 7 and 8). A toxoid vaccine with and without adjuvant is in phase II trials in patients 18-85 years old to determine efficacy in preventing recurrent CDI in the nine week period after the third dose of this vaccine. Toxoid vaccines typically require repeat administrations and an adjuvant in order to elicit an immune response. Further, their administration is frequently associated with injection site immune reactions. However, toxin-based vaccines only prevent toxin binding, neutralising inflammatory effects; such vaccines are generally unable to prevent colonization completely or clear an existing pathogen from the body. For example, spores may remain meaning that further infection or recurrence of infection with associated symptoms is likely.
Thus there is a need for improved compositions and methods of treating or preventing C. difficile infection. In particular, there is need for polypeptides that will be useful as vaccine components and that may be used to limit or eliminate the colonization—including spores—in vaccinated subjects, further preventing C. difficile transmission. It is an object of the invention to provide polypeptides and compositions which are effective in raising immune responses against C. difficile for use in the development of vaccines for preventing and/or treating C. difficile associated diseases.